Respiratory oxygen consumption measuring device and method

ABSTRACT

A portable apparatus for calculating respiratory oxygen consumption comprising a housing having a fluid inlet, a flow sensor, mounted within the housing, an oxygen sensor and means for calculating the respiratory oxygen consumption using data obtained from the oxygen sensor and the flow sensor. The invention also relates to a method of calculating respiratory oxygen

FIELD OF THE INVENTION

[0001] The present invention relates to methods of and apparatus forcalculation of respiratory oxygen consumption, in particular, althoughnot exclusively, to indirect calorimeters and methods of using the same.

BACKGROUND OF THE INVENTION

[0002] Techniques of calorimetry are used to study the energy ofmetabolism in humans and animals. Calorimetry is used, for example, fordiagnosis of metabolic disorders and for calculating nutritionalrequirements of a subject. Calorimetric measurements can be madedirectly as a measure of heat loss of a subject. Alternatively, indirectmeasurements can be made of a chemical by-product of metabolism.

[0003] A useful measure for nutritionists and sports scientists whenassessing the health and fitness of a subject is the volume of oxygenconsumed at rest and during or after physical exertion.

[0004] Indirect calorimetry often involves measuring the amount ofcarbon dioxide exhaled by a subject, which can in turn be used tocalculate the oxygen consumption of the subject.

[0005] U.S. Pat. No. 5,178,155 discloses an indirect calorimeter thatcomprises a carbon dioxide scrubber arranged to remove carbon dioxidefrom the exhaled gas and in some embodiments from the inhaled gas also.The volume of oxygen consumed can be calculated from the amount ofcarbon dioxide removed from the exhaled gas by the scrubber. Thecalorimeter of U.S. Pat. No. 5,178,155 also comprises two flow meters,the first being arranged to monitor the inhaled gas flow and the exhaledgas flow after removal of the carbon dioxide and the second beingarranged to monitor the exhaled gas flow before removal of the carbondioxide.

[0006] International patent application number PCT/US99/17553 disclosesa method and apparatus for analysing respiratory gases to determineoxygen consumption for indirect calorimetry purposes as well as carbondioxide production by measuring the mass and volume flow rate of inhaledand exhaled gas. The flow measurements are made using known ultrasonicpulse transit time techniques. The gas density may be determined usingacoustic impedance, speed of sound or temperature related techniques.The method involves calculating the oxygen content in the inhaled andexhaled gas. In one embodiment of PCT/US99/17553 measurements are madeon the exhaled gas flow only. In this case, it is necessary to be awareof the oxygen content of the inhaled gas.

[0007] International patent application number PCT/US98/05297 disclosesa calorimeter comprising a flow meter and a capnometer to compute thedifference between the inhaled gas volume and the volume of the exhaledgas less the carbon dioxide volume. The capnometer measures theconcentration of exhaled carbon dioxide. The amount of carbon dioxide inthe exhaled gas can then be subtracted from the total volume of exhaledgas to obtain a value for the volume of exhaled gas excluding carbondioxide. A bidirectional flow mater is also used to measure the flowrate of the inhaled and exhaled gas.

[0008] International patent application number PCT/US91/04587 disclosesa calorimeter comprising means to condition inhaled gas to a temperatureand water vapour comparable with that of the exhaled gas, then thevolume of inhaled gas is measured. Carbon dioxide is removed from theexhaled gas by passing the exhaled gas through a carbon dioxide scrubberand then its volume is measured. A single flow meter may be used tomeasure the volume of both the inhaled and exhaled gas.

[0009] All of the indirect calorimeters described above are complicatedto manufacture and use. It is an aim of preferred embodiments of thepresent invention to provide an alternative method and apparatus forcalculating respiratory oxygen consumption and to provide an alternativeindirect calorimeter and method of using the same.

SUMMARY OF THE INVENTION

[0010] The present invention provides a portable apparatus forcalculating respiratory oxygen consumption comprising a housing having afluid inlet, a flow sensor mounted within the housing, an oxygen sensorand means for calculating respiratory oxygen consumption using dataobtained from the oxygen sensor and the flow sensor.

[0011] By “portable apparatus” we mean an apparatus that is handportable such that it can be carried and used by an individual and canbe hand held in use.

[0012] Suitably, the apparatus is an indirect calorimeter.

[0013] Suitably, the housing is generally tubular. The tubular housingmay have any suitable cross-sectional shape.

[0014] Preferably the flow sensor comprises a movable member, movable byair pressure effected thereupon, and a movement sensor associated withthe movable member.

[0015] Suitably, movement of the movable member within the housing iseffected by passing a fluid into the housing through the fluid inlet.Suitably, the fluid is a gas. Suitably, the gas is exhaled breath.

[0016] The movable member may be a rotatable member, such as a rotor orpaddle wheel, for example.

[0017] Alternatively the movable member may be a plunger, slidablymounted with the housing.

[0018] Suitably, the plunger is arranged to move slidably along thelength of the tubular housing.

[0019] Suitably, there is a substantially fluid tight contact betweenthe periphery of the plunger and the interior surface of the housing.Suitably, the cross-sectional shape of the plunger corresponds with thecross-sectional shape of the interior of the tubular housing.

[0020] Suitably the oxygen sensor is mounted to the housing, preferablywithin the housing.

[0021] The oxygen sensor may comprise any suitable oxygen sensor. Anexample of a suitable oxygen sensor is an MOX-1 (trade mark) sensoravailable from City Technology Limited of Portsmouth, England.

[0022] Suitably, when the movable member comprises a plunger the oxygensensor is attached to an end of the plunger. Preferably, the oxygensensor is attached to an end of the plunger that is nearest the fluidinlet.

[0023] The oxygen sensor may be either directly or indirectly attachedto the surface of the movable member. Alternatively, or in addition theoxygen sensor may be embedded in the movable member.

[0024] Alternatively, or in addition the oxygen sensor may be separatefrom the movable member.

[0025] The movement sensor is, suitably, arranged to measure the speedof movement of the movable member during use of the apparatus accordingto the invention.

[0026] Any suitable movement sensor may be used. For example, themovement sensor may comprise one or more sensor switches. Suitablesensor switches include a slotted opto switch number 304-560 availablefrom RS Components Limited of Corby, England.

[0027] Suitably, the movement sensor is attached, either directly orindirectly, to the movable member. Preferably, a movement sensor isembedded in the movable member.

[0028] The movement sensor may comprise a first switch located on themovable member and a second switch located on the housing.

[0029] If the movable member is a rotor or paddle wheel, there may beplurality of first switches, each mounted on a separate blade of themotor, and a second switch located on the housing.

[0030] Suitably, the apparatus for calculating respiratory oxygenconsumption is arranged such that the movable member moves only apre-set distance within the housing during use. Suitably, the movablemember moves between a start position and an end position.

[0031] The apparatus for calculating respiratory oxygen consumption mayfurther comprise a fluid outlet. Suitably, when the movable member is aplunger the fluid outlet is located adjacent the end position of theplunger. Suitably, the fluid outlet is positioned such that excessexhaled breath passes out of the housing through the fluid outlet oncethe plunger reaches the end position and does not cause continuedmovement of the plunger within the housing.

[0032] The apparatus may further comprise a collection chamber. Thecollection chamber may be in direct or indirect fluid flow communicationwith the fluid outlet. The collection chamber may comprise any suitabledevice, for example a bag or box. Suitably, the oxygen sensor is locatedin the collection chamber. Suitably the collection chamber forms part ofthe housing of the apparatus and is therefore integral with the housing.

[0033] If the movement sensor comprises a first switch located on themovable member and a second switch located in the housing, the secondswitch is suitably located adjacent the fluid outlet. Suitably, thesecond switch is located downstream of the fluid outlet relative to thefluid inlet. When the movable member is a plunger, suitably the secondswitch is located at the end position of the plunger.

[0034] When the movable member is a plunger the apparatus in accordancewith the present invention may comprise means to return the plunger tothe start position. Suitably, the apparatus comprises means to returnthe plunger to the start position after calculation of the respiratoryoxygen consumption has been made. Any suitable means of returning theplunger to the start position may be used, for example a spring.

[0035] The fluid inlet is suitably arranged to allow ingress of exhaledbreath from a subject using the apparatus into the apparatus. The fluidinlet may be provided by the end of the housing.

[0036] Suitably, apparatus in accordance with the present inventioncomprises a mouthpiece associated with the fluid inlet. The fluid inletmay be provided by the mouthpiece. Alternatively, the fluid inlet may beseparate from the mouthpiece. If the mouthpiece is separate from thefluid inlet, the mouthpiece is suitably directly connected to the fluidinlet.

[0037] The apparatus according to the present invention may comprise anopening in the housing. Suitably, the opening provides for externalfluid to be inhaled through the apparatus by the subject using theapparatus. The opening may be sealed by a one way valve, which valveallows fluid to be inhaled through the opening but prevents exhaledfluid from passing through the opening. Suitably, substantially nomovement of the movable member occurs when fluid is inhaled through theopening by the subject. If the movable member is a plunger, suitably theopening is located between the fluid inlet and the end of the plungerwhen the plunger is located in the start position.

[0038] The apparatus in accordance with the present invention maycomprise any suitable means for calculating the respiratory oxygenconsumption. For example, the apparatus may comprise a computer or otherelectronic device for calculating the respiratory oxygen consumption.The means for calculating the respiratory oxygen consumption may bemounted on the housing of the apparatus or detachably connected to thehousing.

[0039] The present invention further provides a method of calculatingrespiratory oxygen consumption comprising the following steps:

[0040] (a) passing an exhaled breath into a housing;

[0041] (b) measuring the fraction of oxygen in the exhaled breath usingan oxygen sensor;

[0042] (c) measuring the time taken to exhale the breath using a flowsensor mounted within the housing; and

[0043] (d) calculating the oxygen consumption using the data obtained insteps b and c.

[0044] Suitably, step (a) comprises passing an exhaled breath of knownvalue into the housing.

[0045] Suitably the flow sensor comprises a movable member associatedwith a movement sensor and step (a) comprises passing an exhaled breathinto a housing to cause movement of a movable member.

[0046] Suitably, the method of calculating respiratory oxygenconsumption is a method of indirect calorimetry.

[0047] The method of the present invention may be carried out using theportable apparatus of the present invention.

[0048] When the apparatus comprises a movable member, suitably thevolume of the exhaled breath is calculated by measuring the extent ofmovement of the movable member.

[0049] When the movable member is a plunger, suitably the volume of theexhaled breath is calculated by measuring the distance moved by theplunger.

[0050] The range of movement of the movable member within the housingmay be restricted to a pre-set distance.

[0051] Alternatively, movement of the movable member is not restrictedbut the movement sensor and the oxygen sensor are arranged to takemeasurements only during movement of the movable member over arestricted movement range.

[0052] In both cases, measurements are made using the oxygen sensor andthe movement sensor only for the duration of exhalation of a knownvolume of breath.

[0053] The method may be repeated one or more times to obtain an averagecalculation of oxygen consumption. If the method is repeated one or moretimes, the results are suitably integrated to provide an average figure.

[0054] The apparatus of the present invention and the method of thepresent invention may use the following formula to calculate therespiratory oxygen consumption per breath exhaled:

VO ₂ =K×(F _(i) O ₂ −F _(e) O ₂)×V×(30/t)×C  Formula I

[0055] Where,

[0056] VO₂ is the respiratory oxygen consumption of the subject

[0057] F_(i)O₂ is the fraction of inhaled oxygen

[0058] F_(e)O₂ is the fraction of exhaled oxygen

[0059] V is the volume of the exhaled breath over which the measurementsare taken

[0060] t is the time taken to exhale the known volume of breath

[0061] C is the constant calorific value for oxygen (approximately 5kcal).

[0062] K is a constant allowing for calibration.

[0063] The fraction of inhaled oxygen can be calculated from the gasinhaled by the subject. For instance, if the subject inhaled atmosphericair, the fraction of inhaled oxygen can either be assumed to be thestandard value of 20.94%, or the actual fraction of oxygen in theatmospheric air can be measured using any known technique.

[0064] The fraction of exhaled oxygen is measured using the oxygensensor.

[0065] The volume of the exhaled breath can be measured by any suitablemethod. Suitably, when the apparatus comprises a movable member, themovable member moves a known extent within the housing and this distanceis used to measure the volume of the exhaled breath in respect of whichmeasurements are taken. If the oxygen sensor is attached to the surfaceof the movable member the volume calculation must take into account thevolume reduction caused by the presence of the oxygen sensor.

[0066] Suitably, in use, the movable member is arranged in the housingat a start position at which a first switch of a movement sensor isspaced apart from a second switch of the movement sensor. When exhaledbreath passes into the housing the movable member suitably moves towardsthe second switch. Preferably, the movement sensor takes a measurementduring movement of the first sensor from its start position until thefirst sensor reaches the position of the second sensor. In this way, themovement sensor takes measurements only for the duration of exhalationof a breath.

[0067] During exhalation of the breath the oxygen sensor measures thefraction of molecular oxygen in the exhaled breath.

[0068] The data obtained from the oxygen sensor and the flow sensor maythen be used to calculate the oxygen consumption of the subject perbreath using Formula I.

[0069] If the apparatus in accordance with the present inventioncomprises electronic means to calculate the oxygen consumption, theoxygen sensor and the flow sensor suitably transmit the data obtaineddirectly to the electronic calculation means by means of electronicsignals.

[0070] Advantageously, the method and apparatus of the present inventioncan be used to provide information on the oxygen consumption of asubject, for example a human or an animal.

[0071] The apparatus and method of the present invention areadvantageously easy to use. Furthermore, the apparatus of the presentinvention is simple to manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The present invention will now be described, by way of exampleonly, with reference to the following drawings, in which:

[0073]FIG. 1 is a schematic, partially cross sectional, side view ofpart of a portable apparatus in accordance with the present invention,in a start position;

[0074]FIG. 2 is a schematic, partially cross-sectional, side view of theapparatus of FIG. 1 in an end position;

[0075]FIG. 3 is a schematic, partially cross-sectional, side view of apart of an alternative embodiment of a portable apparatus in accordingwith the present invention, in a start position;

[0076]FIG. 4 is a schematic, partially cross-sectional, side view of theapparatus of FIG. 3 in an end position; and

[0077]FIG. 5 is a schematic, partially cross-sectional side view of asecond embodiment of a portable apparatus in accordance with the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0078]FIGS. 1 and 2 show part of a portable apparatus for calculatingrespiratory oxygen consumption 2 comprising a housing 4, a plunger 6, anoxygen sensor 8 and a movement sensor provided by a first switch 10 anda second switch 12. The apparatus 2 further comprises electroniccalculation means 14.

[0079] The plunger 6 is slidably movable inside the housing 4, theinterior of the housing 4 and the plunger 6 having the samecross-sectional shape. The relative dimensions of the periphery of theplunger 6 and the interior of the housing 4 being arranged such thatthere is a substantially fluid tight fit between the periphery of theplunger 6 and the interior of the housing 4.

[0080] The housing 4 comprises a fluid inlet 16 and a fluid outlet 18.

[0081] The oxygen sensor 8 is embedded in the end 20 of the plunger 6.The oxygen sensor is electrically connected to the electricalcalculation means 14 by wire 22.

[0082] The first switch 10 of the movement sensor is embedded in a sideof the plunger 4. The second switch 12 of the movement sensor isembedded in the interior wall of the housing 4. A wire 24 connects thefirst switch 10 with the electrical calculation means 14 and a wire 26connects the second switch 12 with the electrical calculation means 14.

[0083] In use of the apparatus 2, the plunger 6 is arranged in thehousing 4 at the start position as shown in FIG. 1. An exhaled breath isguided into the fluid inlet 16 of the housing 4. The end of the housing4 providing the fluid inlet 16 may act as a mouthpiece for the apparatus2. Alternatively, a separate mouthpiece (not shown) may be directly orindirectly connected to the housing 4.

[0084] The exhaled breath causes the plunger 6 to move away from thefluid inlet 16. The plunger 6 will continue to move in this directionuntil the end 20 of the plunger 6 passes the fluid outlet 18 to reachthe end position as shown in FIG. 2. Thereafter, excess exhaled breathwill pass out of the fluid outlet 18 and movement of the plunger 6 willcease.

[0085] Whilst the plunger 6 is moving from the start position to the endposition, the oxygen sensor 8 is measuring the fraction of oxygen in theexhaled breath. The oxygen sensor 8 sends information of the measurementto the electrical calculation means 14 in the form of an electricalsignal by means of wire 22.

[0086] During movement of the plunger 6 from the start position to theend position, the switches 10, 12 of the movement sensor measure thetime taken to move this set distance. This time is a measurement of thetime taken to exhale a known volume of breath. The switches 10, 12 sendthe measurement to the electrical calculation means 14 using wires 24and 26.

[0087] The electrical calculation means 14 is programmed to calculatethe oxygen consumption of the subject in accordance with Formula I setout above. In order to make this calculation the operator will need toinsert details for the fraction of oxygen in the inhaled gas. This maybe the standard value for the oxygen content of air, in this case, thisinformation may be previously programmed into the electrical calculationmeans 14. If the oxygen fraction in the inhaled air is measured, themeasured value will need to be input into the electrical calculationmeans 14 before the calculation can be made.

[0088] The method and calculation outlined above may be repeated one ormore times, and the results may be integrated to provide an averagevalue for the oxygen consumption.

[0089] The portable apparatus 2 is of a size and configuration such thatit can be held and carried in the hand by an individual and connected tothe electrical calculation means when desired.

[0090]FIGS. 3 and 4 show part of an alternative portable apparatus forcalculating respiratory oxygen consumption 50, comprising a housing 52and a plunger 54.

[0091] The housing 52 comprises an opening 56 to allow ingress ofexternal air. The opening 56 is covered by a one way valve 58, whichvalve 58 allows ingress through opening 56 of air but prevents egress ofair through opening 56.

[0092] The housing 52 further comprises a fluid inlet 60 which allowsinhaled external air to pass from the opening 56 to the subject (notshown) using the apparatus. The fluid inlet 60 also allows exhaledbreath to pass into the housing 52.

[0093] The housing 52 also comprises a gas outlet 62, which allowsexhaled breath to pass out of the housing 62. The gas outlet 62 isconnected to a gas collection box 64 by means of a flexible tube 66.

[0094] The apparatus 50 further comprises an oxygen sensor 68, locatedin the collection box 64, and a movement sensor provided by first andsecond switches 70, 72. The first switch 70 is embedded in the plunger54. The second switch 72 is embedded in the wall of the housing 52,downstream of the gas outlet 62.

[0095] The oxygen sensor 68 and the switches 70, 72 are connected to acalculation means (not shown) by wires 74.

[0096] In use of the apparatus 50, the plunger 54 is arranged in thehousing 52 at the start position as shown in FIG. 3.

[0097] A subject inhales external air through the opening 56 and thefluid inlet 60. The subject then exhales breath into the housing 52 viathe fluid inlet 60.

[0098] The exhaled breath causes the plunger 54 to move away from thefluid inlet 60. The plunger 54 will continue to move in this directionuntil the end 76 of the plunger 54 passes the gas outlet 62 to reach theend position shown in FIG. 4. Thereafter, excess exhaled breath willpass out of the outlet 62 and into the collection box 64, and movementof the plunger 54 will cease.

[0099] During movement of the plunger 54 from the start position to theend position the switches 70, 72 measure the time taken to move this setdistance. The measurement is sent to the calculation means (not shown)along wires 74.

[0100] The oxygen sensor 68 measures the oxygen content of the exhaledbreath in the collection box 64, and sends the measurement to thecalculation means (not shown) by means of wires 74.

[0101] The calculation means calculates the oxygen consumption inaccordance with formula I set out above. The calculation is made in thesame way as described above in relation to FIGS. 1 and 2.

[0102] We refer now to FIG. 5. FIG. 5 shows part of a portable apparatusfor calculating respiratory oxygen consumption (2) comprising a housing(77), a rotor (80) comprising a rotor hub (82) from which extend eightrotor blades (84), an oxygen sensor (78) and a movement sensor providedby a first switch (86) mounted in the housing (77). The apparatus (2)further comprises electronic calculation means (14). The rotor (80) ismounted such that the rotor hub extends horizontally and perpendicularto the longitudinal direction of the housing (77). The rotor (80) isoriented such that the rotor blades (84) operably cooperate with thefirst switch (86) when the rotor rotates within the housing. Thus, eachof the eight rotor blades (84) will sequentially operably cooperate withthe first switch (86) as the rotor (80) rotates.

[0103] The housing (77) comprises a fluid inlet (82) and two fluidoutlets in the form of vents (84). The fluid inlet is located at one endof the housing (77), with the vents (84) located at the other endthereof. The oxygen sensor (78) is embedded at the end of the housing(77) in which the vents (84) are located, downstream of the fluid inlet(82). The oxygen sensor (78) is electrically connected to electricalcalculation means (14) by wires (79).

[0104] The first switch (86) is located in the housing (77), adjacent tothe rotor (80), such that as the rotor rotates, the rotor blades (84)are arranged to move past the first switch (86) to thereby operablycooperate with the first switch (86). A wire (88) connects the firstswitch (86) to the electrical calculation means (14).

[0105] Use of the apparatus (2) of FIG. 5 will now be described. Anexhaled breath is guided into the fluid inlet (82) of the housing (77).The end of the housing (77) providing the fluid inlet (82) may act as amouthpiece for the apparatus (2). Alternatively, a separate mouthpiece(not shown) may be directly or indirectly connected to the housing (77).The exhaled breath causes the rotor (80) to rotate about the rotor hub(82), thereby causing rotational movement of the eight rotor blades (84)around the rotor hub (82). Whilst the rotor (80) is rotating, the oxygensensor (78) measures the fraction of oxygen in the exhaled breathpassing over the rotor blades (84) and to the oxygen sensor (78). Theoxygen sensor (78) sends information of the measurement to theelectrical calculation means (14) in the form of an electrical signal bymeans of wires (79).

[0106] During movement of the rotor (80), the first switch (86) measuresthe time taken between adjacent rotor blades (84) passing over the firstswitch (86) of the movement sensor. The first switch (86) also recordsinformation as to the total number of rotor blades (84) which pass thefirst switch (86) during an exhaled breath. The time taken betweenadjacent rotor blades (84) passing the first switch (86), and the totalnumber of rotor blades (84) passing the first switch (86) is ameasurement of the time taken to exhale a known volume of breath. Thefirst switch (86) sends the measurement to the electrical calculationmeans (14) through the wire (88).

[0107] The electrical calculation means (14) is programmed to calculatethe oxygen consumption of the subject in accordance with Formula I setout above. The calculation is made in the same way as described above inrelation to FIGS. 1 and 2.

[0108] The reader's attention is directed to all papers and documentswhich are filed concurrently with or previous to this specification inconnection with this application and which are open to public inspectionwith this specification, and the contents of all such papers anddocuments are incorporated herein by reference.

[0109] All of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), and/or all of the stepsof any method or process so disclosed, may be combined in anycombination, except combinations where at least some of such featuresand/or steps are mutually exclusive.

[0110] Each feature disclosed in this specification (including anyaccompanying claims, abstract and drawings), may be replaced byalternative features serving the same, equivalent or similar purpose,unless expressly stated otherwise. Thus, unless expressly statedotherwise, each feature disclosed is one example only of a genericseries of equivalent or similar features.

[0111] The invention is not restricted to the details of the foregoingembodiment(s). The invention extend to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

1. A portable apparatus for calculating respiratory oxygen consumptioncomprising a housing having a fluid inlet, a flow sensor, mounted withinthe housing, an oxygen sensor and means for calculating the respiratoryoxygen consumption using data obtained from the oxygen sensor and theflow sensor.
 2. A portable apparatus according to claim 1, which is anindirect calorimeter.
 3. A portable apparatus according to claim 1 or 2wherein the flow sensor comprises a movable member movable by airpressure effected thereupon, and a movement sensor associated with themovable member.
 4. A portable apparatus according to claim 3, whereinthe movable member is a rotatable member.
 5. A portable apparatusaccording to claim 4, wherein the rotatable member is a rotor or paddlewheel.
 6. A portable apparatus according to claim 3, wherein the movablemember is a plunger, slidably mounted with the housing.
 7. A portableapparatus according to any one of claims 3 to 5, wherein in use,movement of the movable member within the housing is effected by passinga fluid into the housing through the fluid inlet.
 8. A portableapparatus according to claim 7, wherein the fluid is exhaled breath. 9.A portable apparatus according to any one of the preceding claims,wherein the oxygen sensor is mounted to the housing.
 10. A portableapparatus according to any one of claims 3-9, wherein the oxygen sensoris attached to an end of the movable member.
 11. A portable apparatusaccording to any one of claims 3-9, wherein the oxygen sensor isseparate from the movable member.
 12. A portable apparatus according toany one of claims 3-11, wherein the movement sensor is arranged tomeasure the speed of movement of the movable member during use of theapparatus.
 13. A portable apparatus according to any one of claims 3-12,wherein the movement sensor comprises one or more sensor switches.
 14. Aportable apparatus according to claim 13, wherein a first switch islocated on the movable member and a second switch is located on thehousing.
 15. A portable apparatus according to any one of claims 3-14,wherein the movable member moves between a start position and an endposition during use.
 16. A portable apparatus according to any one ofthe preceding claims, comprising a fluid outlet.
 17. A portableapparatus according to claim 16, wherein the movable member is aplunger, slidably mounted within the housing and the fluid outlet isadjacent the end position of the plunger.
 18. A portable apparatusaccording to any one of the preceding claims, comprising a collectionchamber.
 19. A portable apparatus according to claim 18, wherein thecollection chamber is in fluid flow communication with the fluid outlet.20. A portable apparatus according to claim 18 or 19, wherein the oxygensensor is located in the collection chamber.
 21. A portable apparatusaccording to any one of the preceding claims, wherein the fluid inlet isprovided by the end of the housing.
 22. A portable apparatus accordingto any one of the preceding claims comprising a mouthpiece associatedwith the fluid inlet.
 23. A portable apparatus according to any one ofthe preceding claims, comprising an opening in the housing.
 24. Aportable apparatus according to claim 23, wherein, in use, the openingallows external fluid to be inhaled through the apparatus by the subjectusing the apparatus.
 25. A portable apparatus according to claim 23 or24, wherein the movable member is a plunger, slidably mounted within thehousing, and the opening is located between the fluid inlet and the endof the plunger, when the plunger is located in the start position.
 26. Aportable apparatus according to claim 23, 24 or 25, comprising aone-way-valve to seal the opening.
 27. A portable apparatus according toany one of the preceding claims, wherein the means for calculating therespiratory oxygen consumption comprises a computer or other electricaldevice.
 28. A method of calculating respiratory oxygen consumptioncomprising the following steps: (a) passing an exhaled breath into ahousing; (b) measuring the fraction of oxygen in the exhaled breathusing an oxygen sensor; (c) measuring the time taken to exhale thebreath using a flow sensor mounted within the housing; and (d)calculating the oxygen consumption using the data obtained in (b) and(c).
 29. A method as claimed in claim 28, wherein the flow sensorcomprises a movable member associated with a movement sensor and step(a) comprises passing an exhaled breath into a housing to cause movementof a movable member.
 30. A method according to claim 28 or 29, whereinstep (a) comprises passing an exhaled breath of known volume into thehousing.
 31. A method according to claim 28, 29 or 30, wherein thecalculation of oxygen consumption is carried out using the followingformula: VO ₂ =K×(F _(i) O ₂ −F _(e) O ₂)×V×(30/t)×C  Formula I Where,VO₂ is the respiratory oxygen consumption of the subject F_(i)O₂ is thefraction of inhaled oxygen F_(e)O₂ is the fraction of exhaled oxygen Vis the volume of the exhaled breath over which the measurements aretaken t is the time taken to exhale the known volume of breath C is theconstant calorific value for oxygen (approximately 5 kcal). K is aconstant allowing for calibration.
 32. A method according to any one ofclaims 28-31, comprising a method of indirect calorimetry.
 33. A methodaccording to any one of claims 28-32, wherein the method is carried outon a portable apparatus according to any one of claims 1-27.
 34. Amethod according to any one of claims 29-33, wherein the movable memberis moved within the housing by means of ingress of exhaled air into thehousing.
 35. A method according to any one of claim 29-34, wherein themovable member is arranged to move a pre-set distance within thehousing.
 36. A method according to any one of claims 28-35, whereinsteps (a) to (d) are repeated one or more times to obtain an averagecalculation of oxygen consumption.
 37. Apparatus substantially asdescribed herein and with reference to the drawings hereof.
 38. A methodsubstantially as described herein and with reference to the drawingshereof.